A cobalt silicide (CoSi2) layer may be formed by depositing a cobalt (Co) film on a silicon (Si) film as a wiring of a semiconductor device and heating the Co film. After the CoSi2 layer is formed, a semiconductor wafer (hereinafter, referred to as “wafer”) that is a substrate on which the CoSi2 layer is formed is immersed in a liquid chemical and subjected to wet etching. Accordingly, a residual Co film is completely removed.
Along with the trend toward miniaturization of semiconductor devices, it is considered to use Co as a wiring instead of Cu (copper) that has been conventionally used as a wiring. This is because when Cu is used as a wiring, a barrier film needs to be formed around a Cu wiring to prevent diffusion of metal atoms of the wiring to an insulating film around the wiring, whereas when Co is used as a wiring, the wiring itself serves as a barrier film, which makes it unnecessary to additionally form a barrier film.
In order to form a fine Co wiring, etching of a Co film needs to be controlled with high accuracy. Specifically, it is considered to etch the Co film such that variation of an etching amount in a surface of a wafer becomes 1 nm or less; to control roughness on a surface of the etched Co film; and to selectively etch the Co film. Since the wet etching is not suitable for controlling the etching with high accuracy, it is considered to etch the Co film by using a gas.
For example, Japanese Patent Application Publication No. 2015-12243 (paragraphs 0030 to 0035) discloses that a Co film, on a substrate heated to 200° C. to 400° C., is etched by simultaneously supplying O2 gas and a hexafluoroacetylacetonate (Hfac) gas, β-diketone gas, such that a flow rate ratio of the O2 gas to the Hfac gas becomes 1% or less. The O2 gas serves as an oxidizing gas for oxidizing the Co film. The Hfac gas serves an etching gas for generating a complex having a comparatively low vapor pressure by reaction with the oxidized Co film and then removing an oxide of the Co film. Japanese Patent Application Publication No. 2015-19065 (paragraphs 0035 and 0036) discloses that a Co film is etched by using an Hfac gas that may be added with O2 gas. Further, Japanese Patent No. 2519625 (paragraphs 0035 and 0036) discloses that a metal contaminant such as copper or the like on a surface of a substrate is removed by reaction with β-diketone in an oxidizing atmosphere.
It has been confirmed by the present inventors that when the Co film formed on the surface of the substrate is etched by supplying both the O2 gas and the Hfac gas to the substrate, the Hfac gas is decomposed even at a comparatively low temperature due to the catalytic effect of Co and oxidized Co and the action of the O2 gas, and a film mainly containing carbon (hereinafter, referred to as “carbon film”) remained on the processed substrate. Japanese Patent Application Publication No. 2015-12243 discloses that the O2 gas and the Hfac gas are simultaneously supplied to the wafer while heating the substrate to a comparatively high temperature ranging from 300° C. to 400° C. In that case, the carbon film is formed; however, Japanese Patent Application Publication No. 2015-12243 does not pay attention to the formation of the carbon film by the Hfac gas, and cannot solve the problem of the formation of the carbon film. In addition, a solution to the above problem is not disclosed in Japanese Patent Application Publication No. 2015-19065 and Japanese Patent No. 2519625.